i) Field of the Invention
The present invention relates to a magnetoresistive head for utilizing a resistance change in accordance with an external magnetic field intensity to detect the external magnetic field intensity, and an information regeneration apparatus for regenerating information recorded in a recording medium.
ii) Description of Related Art
In recent years, with spread of a computer, a large amount of information has been handled in a daily manner. Such information is usually recorded on a recording medium as a large number of physical marks, and regenerated by an information regeneration apparatus for reading the mark on the recording medium to regenerate an electric regeneration signal.
A hard disk drive (HDD) is one of the information regeneration apparatuses, and is characterized in that a memory capacity is large and access speed to the information is fast. The HDD is generally provided with a magnetic disk as the recording medium whose surface is formed of a magnetic material, and a regeneration head for regenerating the information recorded on the magnetic disk. For the magnetic disk, a surface is magnetized for each micro area (one-bit region), and one bit of information is recorded in a form of a magnetization direction of the one-bit region. The regeneration head is disposed in the vicinity of the magnetic disk, and outputs an electric regeneration signal in accordance with a signal magnetic field Hsig generated from the magnetization of the one-bit region of the magnetic disk to regenerate the information recorded on the magnetic disk.
A recording density of the magnetic disk continues to be enhanced year by year, an area of the one-bit region decreases with enhancement of the recording density, and the signal magnetic field Hsig generated from the one-bit region is weakened. Therefore, a magnetic head for outputting a large regeneration signal is necessary even for this weak signal magnetic field Hsig. As the magnetic head for outputting the large regeneration signal, a spin valve is magnetoresistive head which is a magnetoresistive head utilizing a giant magnetoresistive (GMR) effect starts to be put to practical use in earnest. The spin valve magnetoresistive head will be hereinafter referred to as SVMR head.
The SVMR head is provided with a spin valve magnetoresistive film as a multilayered film including a free magnetic layer whose magnetization direction changes in accordance with the external magnetic field, a nonmagnetic layer formed adjacent to the free magnetic layer and provided with conductivity, a pinned magnetic layer formed adjacent to the nonmagnetic layer and having its magnetization direction fixed in a predetermined direction, and an antiferromagnetic layer formed adjacent to the pinned magnetic layer and constituted of an antiferromagnetic material for fixing the magnetization direction of the pinned magnetic layer. For the magnetoresistive film, a resistance change is caused in accordance with a relative angle change of magnetization directions of the free magnetic layer and fixed magnetic layer, a resistivity is minimized when the magnetization directions are directed in the same direction, and the resistivity is maximized when magnetizations are directed in opposite directions. The magnetoresistive film is provided with a pair of electrode terminals, and during operation a sense current is passed through the magnetoresistive film from the pair of electrode terminals. While the sense current flows, and the SVMR head is disposed close to a magnetic disk and relatively moved, an electric resistivity of the magnetoresistive film successively changes in accordance with a signal magnetic field Hsig from the magnetic disk, and a regeneration signal with an output voltage represented by a product of the electric resistivity and the sense current value is outputted.
An output of the regeneration signal of the SVMR head is substantially proportional to a difference xcex94xcfx81/t between a maximum value and a minimum value of a sheet resistance which changes in accordance with the external magnetic field. The difference xcex94xcfx81/t between the maximum value and the minimum value of the changing sheet resistance will be hereinafter referred to as resistance change xcex94xcfx81/t. In general, since the spin valve magnetoresistive film has a large resistance change xcex94xcfx81/t, the high-output regeneration signal is outputted by the SVMR head. However, it is demanded that a higher output be obtained from the SVMR head by further increasing the resistance change xcex94xcfx81/t. It is known that in order to increase the resistance change xcex94xcfx81/t, thickness of the free magnetic layer and nonmagnetic layer may be reduced. When the thickness of the layer is large, an excess shunt current not contributing to the magnetoresistive effect flows in these layers to decrease the resistance change xcex94xcfx81/t, but a shunt current amount is suppressed by setting these layers to be thin.
However, in the magnetoresistive film, an interlayer coupling field Hin attributed to exchange coupling of the magnetizations is applied to the magnetization of the free magnetic layer mainly from the magnetization of the pinned magnetic layer, and with advancement of thinning of the free magnetic layer and nonmagnetic layer, this interlayer coupling field Hin increases. For example, the resistance change xcex94xcfx81/t of the spin valve magnetoresistive film constituted of Ta (50 angstroms)/CoFe (free magnetic layer: 20 angstroms)/Cu (nonmagnetic layer: 30 angstroms)/CoFe (pinned magnetic layer: 20 angstroms)/PtMn (antiferromagnetic layer: 200 angstroms)/Ta (100 angstroms) is about 0.9xcexa9, but the resistance change xcex94xcfx81/t is improved to 1.4xcexa9, by reducing the thickness of the nonmagnetic layer of Cu to 20 angstroms from 30 angstroms. However, by the thickness reduction, the interlayer coupling field Hin increases to 2.5 kA/m from 0.4 kA/m.
When the interlayer coupling field Hin increases in this manner, in a head state, an angle formed by the magnetization directions of the free magnetic layer and pinned magnetic layer fails to ideally form 90 degrees, and a large deviation is caused. In the large deviating state of the angle, the resistance of the magnetoresistive film fails to linearly respond to the change of the signal magnetic field Hsig, and symmetrical property of regeneration waveform of the SVMR head is deteriorated with respect to positive/negative signal magnetic field Hsig. Moreover, the deteriorated symmetrical property results in a decrease of a dynamic range to either one of positive and negative sides of the output voltage, and there arises a problem that a substantial regeneration output decreases.
The present invention has been developed in consideration of the aforementioned situations, and an object thereof is to provide a magnetoresistive head in which an interlayer coupling field Hin applied to a free magnetic layer is minimized, and an information regeneration apparatus provided with the magnetoresistive head.
Among magnetoresistive heads of the present invention for attaining the aforementioned object, a first magnetoresistive head is provided with a magnetoresistive film being a multilayered film including: a pinned magnetic layer having magnetization whose direction is fixed; a free magnetic layer having magnetization whose direction changes in accordance with an external magnetic field; and a first nonmagnetic layer held by the pinned magnetic layer and the free magnetic layer in a layer thickness direction, and indicating a magnitude of resistance in accordance with an angle formed by the magnetization direction of the pinned magnetic layer and the magnetization direction of the free magnetic layer. The magnetoresistive head detects the magnitude of resistance of the magnetoresistive film to detect a strength of the external magnetic field.
The magnetoresistive head comprises: a second nonmagnetic layer disposed adjacent to the surface of the free magnetic layer on a side opposite to the surface of the free magnetic layer on a side of the first nonmagnetic layer; and
a bias application layer, disposed adjacent to the surface of the second nonmagnetic layer on a side opposite to the surface of the second nonmagnetic layer on the side of the free magnetic layer, for applying, to the free magnetic layer, a bias magnetic field generated by a static interlayer coupling and directed in a direction opposite to the magnetization direction of the pinned magnetic layer. The bias application layer comprises a material including at least one of an antiferromagnetic material of an ordered form and a hard magnetic material.
As described in the related art, an interlayer coupling field is generally applied to the free magnetic layer from the pinned magnetic layer. Moreover, the interlayer coupling field also includes the bias magnetic field applied to the free magnetic layer from the bias application layer referred to in the present invention. The interlayer coupling field applied to the free magnetic layer as described later is a sum of the interlayer coupling fields applied to the free magnetic layer from the pinned magnetic layer and bias application layer.
When the bias application layer for applying the bias magnetic field to the free magnetic layer is formed as in the first magnetoresistive head of the present invention, a magnitude of the interlayer coupling field applied to the free magnetic layer is reduced by the bias magnetic field.
Moreover, when the bias application layer comprises the material including at least one of the antiferromagnetic material of the ordered form and the hard magnetic material, as described later in an embodiment, reduction of the interlayer coupling field applied to the free magnetic layer is steadily performed. Furthermore, the bias application layer may include a ferrimagnetic material in addition to at least one of the aforementioned magnetic materials.
In the first magnetoresistive head of the present invention, the first nonmagnetic layer preferably comprises copper or an alloy including copper and has a thickness of 26 angstroms or less.
When the first nonmagnetic layer has such thickness, reduction of the interlayer coupling field applied to the free magnetic layer is especially effectively performed.
Moreover, in the first magnetoresistive head of the present invention, the second nonmagnetic layer preferably comprises copper or the alloy including copper and has a thickness in a range of 5 angstroms to 20 angstroms.
In the first magnetoresistive head, as described later in the embodiment and an example, while a large resistance change xcex94xcfx81/t is kept, the interlayer coupling field applied to the free magnetic layer can be reduced to indicate an appropriate value.
Among the magnetoresistive heads of the present invention for attaining the aforementioned object, a second magnetoresistive head is provided with a magnetoresistive film being a multilayered film including: a pinned magnetic layer having magnetization whose direction is fixed; a free magnetic layer having magnetization whose direction changes in accordance with an external magnetic field; and a first nonmagnetic layer held by the pinned magnetic layer and the free magnetic layer in a layer thickness direction, and indicating a magnitude of resistance in accordance with an angle formed by the magnetization direction of the pinned magnetic layer and the magnetization direction of the free magnetic layer. The magnetoresistive head detects the magnitude of resistance of the magnetoresistive film to detect a strength of the external magnetic field.
The magnetoresistive head comprises:
a second nonmagnetic layer disposed on a side of the free magnetic layer opposite to the first nonmagnetic layer; and
a bias application layer, disposed on a side of the second nonmagnetic layer opposite to the free magnetic layer, for applying, to the free magnetic layer, a bias magnetic field generated by a static interlayer coupling, directed in a direction opposite to the magnetization direction of the pinned-magnetic layer and having a strength of 800 A/m or more.
When the bias application layer for applying the bias magnetic field with the strength of 800 A/m or more to the free magnetic layer is formed as in the second magnetoresistive head of the present invention, as described later in the embodiment, the magnitude of the interlayer coupling field applied to the free magnetic layer is effectively reduced by the bias magnetic field.
Moreover, in the second magnetoresistive head of the present invention, the bias application layer comprises at least one material of a material group consisting of an ordered form antiferromagnetic material, a hard magnetic material, and a ferrimagnetic material.
When the bias application layer comprises such material, as described later in the embodiment, the reduction of the interlayer coupling field applied to the free magnetic layer is steadily performed.
Among the magnetoresistive heads of the present invention for attaining the aforementioned object, a third magnetoresistive head is provided with a magnetoresistive film being a multilayered film including:
a first pinned magnetic layer having magnetization whose direction is fixed;
a first nonmagnetic layer formed on the first pinned magnetic layer;
a free magnetic layer formed on the first nonmagnetic layer, and provided with a first soft magnetic layer and a second soft magnetic layer formed of a soft magnetic material and an antiparallel coupling middle layer, formed between the soft magnetic layers, for coupling magnetizations of the soft magnetic layers in opposite directions, in which the magnetization directions of the soft magnetic layers coupled in the opposite directions change in accordance with an external magnetic field;
a second nonmagnetic layer formed on the free magnetic layer; and
a second pinned magnetic layer formed on the second nonmagnetic layer and provided with magnetization fixed in the same direction as the magnetization direction of the first pinned magnetic layer, and indicating a magnitude of resistance in accordance with an angle formed by the magnetization direction of the first pinned magnetic layer and the magnetization direction of the first soft magnetic layer. The third magnetoresistive head detects the magnitude of resistance of the magnetoresistive film to detect a strength of the external magnetic field.
In the third magnetoresistive head of the present invention, as described later in the embodiment, since the magnetic field applied to the first soft magnetic layer from the first pinned magnetic layer, and the magnetic field applied to the second soft magnetic layer from the second pinned magnetic layer are substantially mutually offset, an influence by the excessive magnetic field applied to the free magnetic layer is reduced.
Among information regeneration apparatuses of the present invention for attaining the aforementioned object, a first information regeneration apparatus is provided with a magnetic head, disposed in the vicinity of or in contact with a magnetic recording medium on which information is recorded by a magnetization direction, for detecting the magnetization direction of each point of the magnetic recording medium, and regenerates the information in accordance with the magnetization direction of each point of the magnetic recording medium detected by the magnetic head.
The magnetic head is provided with a magnetoresistive film being a multilayered film including: a pinned magnetic layer having magnetization whose direction is fixed; a free magnetic layer having magnetization whose direction changes in accordance with an external magnetic field; and a first nonmagnetic layer held by the pinned magnetic layer and the free magnetic layer in a layer thickness direction, and indicating a magnitude of resistance in accordance with an angle formed by the magnetization direction of the pinned magnetic layer and the magnetization direction of the free magnetic layer. The magnetic head detects the magnitude of resistance of the magnetoresistive film to detect a strength of the external magnetic field.
The magnetic head comprises: a second nonmagnetic layer disposed adjacent to the surface of the free magnetic layer on a side opposite to the side of the first nonmagnetic layer; and
a bias application layer, disposed adjacent to the surface of the second nonmagnetic layer on a side opposite to the side of the free magnetic layer, for applying, to the free magnetic layer, a bias magnetic field generated by a static interlayer coupling and directed in a direction opposite to the magnetization direction of the pinned magnetic layer. The bias application layer comprises a material including at least one of an antiferromagnetic material of an ordered form and a hard magnetic material.
Since the first information regeneration apparatus employs the first magnetoresistive head of the present invention as the magnetic head, and the interlayer coupling field applied to the free magnetic layer is reduced, a symmetrical property of a regeneration waveform is high, and a regeneration output is large.
Among the information regeneration apparatuses of the present invention for attaining the aforementioned object, a second information regeneration apparatus is provided with a magnetic head, disposed in the vicinity of or in contact with a magnetic recording medium on which information is recorded by a magnetization direction, for detecting the magnetization direction of each point of the magnetic recording medium, and regenerates the information in accordance with the magnetization direction of each point of the magnetic recording medium detected by the magnetic head.
The magnetic head is provided with a magnetoresistive film being a multilayered film including: a pinned magnetic layer having magnetization whose direction is fixed; a free magnetic layer having magnetization whose direction changes in accordance with an external magnetic field; and a first nonmagnetic layer held by the pinned magnetic layer and the free magnetic layer in a layer thickness direction, and indicating a magnitude of resistance in accordance with an angle formed by the magnetization direction of the pinned magnetic layer and the magnetization direction of the free magnetic layer. The magnetic head detects the magnitude of resistance of the magnetoresistive film to detect a strength of the external magnetic field.
The magnetoresistive head comprises:
a second nonmagnetic layer disposed on a side of the free magnetic layer opposite to the first nonmagnetic layer; and
a bias application layer, disposed on a side of the second nonmagnetic layer opposite to the free magnetic layer, for applying, to the free magnetic layer, a bias magnetic field generated by a static interlayer coupling, directed in a direction opposite to the magnetization direction of the pinned magnetic layer and having a strength of 800 A/m or more.
Since the second information regeneration apparatus employs the second magnetoresistive head of the present invention as the magnetic head, and the interlayer coupling field applied to the free magnetic layer is reduced, the symmetrical property of the regeneration waveform is high, and the regeneration output is large.
Among the information regeneration apparatuses of the present invention for attaining the aforementioned object, a third information regeneration apparatus is provided with a magnetic head, disposed in the vicinity of or in contact with a magnetic recording medium on which information is recorded by a magnetization direction, for detecting the magnetization direction of each point of the magnetic recording medium, and regenerates the information in accordance with the magnetization direction of each point of the magnetic recording medium detected by the magnetic head.
The magnetic head is provided with a magnetoresistive film being a multilayered film including:
a first pinned magnetic layer having magnetization whose direction is fixed;
a first nonmagnetic layer formed on the first pinned magnetic layer;
a free magnetic layer formed on the first nonmagnetic layer, and provided with a first soft magnetic layer and a second soft magnetic layer formed of a soft magnetic material and an antiparallel coupling middle layer, formed between the soft magnetic layers, for coupling magnetizations of the soft magnetic layers in opposite directions, in which the magnetization directions of the soft magnetic layers coupled in the opposite directions change in accordance with an external magnetic field;
a second nonmagnetic layer formed on the free magnetic layer; and
a second pinned magnetic layer formed on the second nonmagnetic layer and provided with magnetization fixed in the same direction as the magnetization direction of the first pinned magnetic layer, and indicating a magnitude of resistance in accordance with an angle formed by the magnetization direction of the first pinned magnetic layer and the magnetization direction of the first soft magnetic layer. The magnetic head detects the magnitude of resistance of the magnetoresistive film to detect a strength of the external magnetic field.
Since the third information regeneration apparatus employs the third magnetoresistive head of the present invention as the magnetic head, and the interlayer coupling field applied to the free magnetic layer is substantially reduced, the symmetrical property of the regeneration waveform is high, and the regeneration output is large.